Take a two-slit diffraction experiment. From what I've read or gathered, it is supposed to be caused by the geometry of the setup, and the frequency of the light (maybe a few more things). But, it is talked about in terms of the geometry, and no cause attributed to interactions between the light and the corners of the slits. I've even had someone tell me it couldn't be an interaction between the light and corners of the slits. And even using electrons instead of light, it's still talked about the same; as the geometry and not about the electrons interacting with the substance of the slits. But, when you probe a substance with an electron source, say like an electron microscope, it's clearly (to me at least) talked about in the sense of the electrons interacting with the substance being probed, and that the cause of the diffraction pattern. I find these two things inconsistent; one an interaction and the other not. How is it again that we know (if I don't have my facts mistaken) the diffraction pattern of a two-slit experiment is not caused by interactions between the light/electrons and the sides of the slits?